Field of the Invention
The present disclosure relates to compounds and methods for inhibition of indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO); further the disclosure relates to method of treatment of diseases and disorders mediated by tryptophan deficiency.
Summary of the Related Art
Tryptophan (Trp) is an essential amino acid required for the biosynthesis of proteins, niacin and the neurotransmitter 5-hydroxytryptamine (serotonin). The enzymes indoleamine 2,3-dioxygenase 1 (also known as INDO1 or IDO1), indoleamine-2,3-dioxygenase 2 (INDOL1 or IDO2) and tryptophan-2,3-dioxygenase (TDO) catalyze the first and rate limiting step in the degradation of L-tryptophan to N-formyl-kynurenine. Although these enzymes catalyze the same reaction, compartmentalization of IDO and TDO is thought to mediate their different biological roles. IDO1 is normally expressed in cells of the gastrointestinal and pulmonary epithelia, epididymus, placenta, pDCs in draining lymph nodes and tumor cells. IDO2 is expressed mainly in brain and placenta, but certain splice variants are also detected in liver, small intestine, spleen, placenta, thymus lung, brain, kidney and colon. TDO is expressed mainly in liver, and controls the flux of dietary Trp to the serotonin and kynurenine pathways.
Alignment between IDO1 and IDO2 amino acid sequences reveal highly conserved features that mediate heme and substrate binding. Even though the amino acid sequence identity between IDO1 and IDO2 or IDO1 and TDO are not particularly high, significant residues determined to be important for catalytic activity by IDO and TDO mutagenesis and by crystallographic analysis are highly conserved between IDO1, IDO2 and TDO, suggesting a structural and functional analogy in the mechanism of tryophan deoxygenation. Despite these structural similarities at the active site, IDO1 and TDO have different substrate specificity with TDO being almost exclusively specific for L-Trp and L-Trp derivatives substituted into 5- and 6-positions of the indole group, while IDO1 can accept and oxygenate a wider variety of substrates such as D-Trp, tryptamine, serotonin and 1-methyl-L-Trp.
In human cells, IFN-γ stimulation induces activation of IDO1, which leads to a depletion of Trp, thereby arresting the growth of Trp-dependent intracellular pathogens such as Toxoplasma gondii and Chlamydia trachomatis. IDO1 activity also has an antiproliferative effect on many tumor cells, and IDO1 induction has been observed in vivo during rejection of allogeneic tumors, indicating a possible role for this enzyme in the tumor rejection process.
It has been observed that HeLa cells co-cultured with peripheral blood lymphocytes (PBLs) acquire an immunoinhibitory phenotype through up-regulation of the IDO pathway. A reduction in PBL proliferation upon treatment with interleukin-2 (IL-2) was believed to result from IDO released by the tumor cells in response to IFN-γ secretion by the PBLs. This effect was reversed by treatment with 1-methyl-tryptophan (1MT), a specific IDO inhibitor. It was proposed that IDO activity in tumor cells may serve to impair antitumor responses (Logan, et al., 2002, Immunology, 105: 478-87).
Several lines of evidence suggest that IDO is involved in induction of immune tolerance. Studies of mammalian pregnancy, tumor resistance, chronic infections and autoimmune diseases have shown that cells expressing IDO can suppress T-cell responses and promote tolerance. Accelerated Trp catabolism has been observed in diseases and disorders associated with cellular immune activation, such as infection, malignancy, autoimmune diseases and AIDS, as well as during pregnancy. It was proposed that IDO is induced chronically by HIV infection, and is further increased by opportunistic infections, and that the chronic loss of Trp initiates mechanisms responsible for cachexia, dementia and diarrhea and possibly immunosuppression of AIDS patients (Brown, et al., 1991, Adv. Exp. Med. Biol., 294: 425-35). To this end, it has recently been shown that IDO inhibition can enhance the levels of virus-specific T cells and, concomitantly, reduce the number of virally infected macrophages in a mouse model of HIV (Portula et al., 2005, Blood, 106:2382-90).
IDO is believed to play a role in the immunosuppressive processes that prevent fetal rejection in utero. More than 40 years ago, it was observed that, during pregnancy, the genetically disparate mammalian conceptus survives in spite of what would be predicted by tissue transplantation immunology (Medawar, 1953, Symp. Soc. Exp. Biol. 7: 320-38). Anatomic separation of mother and fetus and antigenic immaturity of the fetus cannot fully explain fetal allograft survival. Recent attention has focused on immunologic tolerance of the mother. Because IDO is expressed by human syncytiotrophoblast cells and systemic tryptophan concentration falls during normal pregnancy, it was hypothesized that IDO expression at the maternal-fetal interface is necessary to prevent immunologic rejection of the fetal allografts. To test this hypothesis, pregnant mice (carrying syngeneic or allogeneic fetuses) were exposed to 1MT, and a rapid, T cell-induced rejection of all allogeneic concepti was observed. Thus, by catabolizing tryptophan, the mammalian conceptus appears to suppress T-cell activity and defends itself against rejection, and blocking tryptophan catabolism during murine pregnancy allows maternal T cells to provoke fetal allograft rejection (Munn, et al., 1998, Science 281: 1191-3).
Further evidence for a tumoral immune resistance mechanism based on tryptophan degradation by IDO comes from the observation that most human tumors constitutively express IDO, and that expression of IDO by immunogenic mouse tumor cells prevents their rejection by preimmunized mice. This effect is accompanied by a lack of accumulation of specific T cells at the tumor site and can be partly reverted by systemic treatment of mice with an inhibitor of IDO, in the absence of noticeable toxicity. Thus, it was suggested that the efficacy of therapeutic vaccination of cancer patients might be improved by concomitant administration of an IDO inhibitor (Uyttenhove et al., 2003, Nature Med., 9: 1269-74). It has also been shown that the IDO inhibitor, 1-MT, can synergize with chemotherapeutic agents to reduce tumor growth in mice, suggesting that IDO inhibition may also enhance the anti-tumor activity of conventional cytotoxic therapies (Muller et al., 2005, Nature Med., 11:312-9).
A similar situation has been observed with TDO. It has been shown that a significant proportion of primary human tumors express elevated levels of TDO or TDO plus IDO (Pilotte et al. 2012, P.N.A.S). Moreover, pharmacological inhibition of TDO activity with TDO inhibitors, leads to immune-mediated rejection of tumors overexpressing TDO, which means that TDO, just as seen in IDO1, can mediate tumor-promoting immunosuppressive effects.
One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. A subset of human IDO-expressing antigen-presenting cells (APCs) that coexpressed CD123 (IL3RA) and CCR6 and inhibited T-cell proliferation have also been described. Both mature and immature CD123-positive dendritic cells suppressed T-cell activity, and this IDO suppressive activity was blocked by 1MT (Munn, et al., 2002, Science 297: 1867-70). It has also been demonstrated that mouse tumor-draining lymph nodes (TDLNs) contain a subset of plasmacytoid dendritic cells (pDCs) that constitutively express immunosuppressive levels of IDO. Despite comprising only 0.5% of lymph node cells, in vitro, these pDCs potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. Thus, it was hypothesized that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses (Munn, et al., 2004, J. Clin. Invest., 114(2): 280-90).
IDO degrades the indole moiety of tryptophan, serotonin and melatonin, and initiates the production of neuroactive and immunoregulatory metabolites, collectively known as kynurenines. By locally depleting tryptophan and increasing proapoptotic kynurenines, IDO expressed by dendritic cells (DCs) can greatly affect T-cell proliferation and survival. IDO induction in DCs could be a common mechanism of deletional tolerance driven by regulatory T cells. Because such tolerogenic responses can be expected to operate in a variety of physiopathological conditions, tryptophan metabolism and kynurenine production might represent a crucial interface between the immune and nervous systems (Grohmann, et al., 2003, Trends Immunol., 24: 242-8).
Small molecule inhibitors of IDO are being developed to treat or prevent IDO-related diseases such as those described above. For example, PCT Publication WO 99/29310 reports methods for altering T cell-mediated immunity comprising altering local extracellular concentrations of tryptophan and tryptophan metabolites, using an inhibitor of IDO such as 1-methyl-DL-tryptophan, p-(3-benzofuranyl)-DL-alanine, p-[3-benzo(b)thienyl]-DL-alanine, and 6-nitro-L-tryptophan) (Munn, 1999). Reported in WO 03/087347, also published as European Patent 1501918, are methods of making antigen-presenting cells for enhancing or reducing T cell tolerance (Munn, 2003). Compounds having indoleamine-2,3-dioxygenase (IDO) inhibitory activity are further reported in WO 2004/094409; WO 2009/073620; WO 2009/132238; WO 2011/056652 and WO 2012/142237. In particular, the compounds of WO 202/142237 encompass a series of trycyclic imidazoisoindoles with potent IDO inhibitory activity.